1. Field of the Invention
This invention relates generally to a system for washing windows and other exterior surfaces of buildings. In particular, it relates to a window washing system which uses substantially pure water to clean such building surfaces, and which uses a novel cable restraint system for restraining an automatic cleaning device against the building surface.
2. Description of the Related Art
Building structures, particularly tall urban buildings, are typically washed manually. A scaffolding structure is usually suspended from the top of the building to be washed. The scaffolding can be raised or lowered so that a person standing on the scaffolding can wash the windows and exterior surfaces of the building by hand. After a vertical section of the building is washed, the scaffolding is repositioned laterally so that the next adjacent vertical section of the building may be cleaned. This procedure may be repeated until the entire building has been washed.
Manual washing of buildings has proven to be quite dangerous, especially with respect to tall skyscrapers. Typical wind and air drafts surrounding a building can exert a significant aerodynamic force upon a scaffolding structure, causing it to swing out and away from the building, and placing persons standing on that scaffolding in peril. Injuries from manual window washing operations are common, and have caused insurance rates to soar. Typically, the cost of insuring a window washing operation can reach 40% of the labor costs. Furthermore, the manual washing of building exteriors is slow and labor-intensive.
Effectively removing mineral deposits from building windows has been a problem which has long plagued the industry. Normal water supplies conventionally used for wash water contain some amount of dissolved solids, including calcium, magnesium, and sodium in the form of bicarbonates, carbonates, chlorides, or sulfates. Regardless of the type or form of the dissolved solids, when a water droplet is allowed to dry on a surface, the solids typically remain as deposits on the surface.
When washing a window, a single water drop left on the surface will typically contain between 300 and 1000 parts per million of dissolved solids, in addition to varying amounts of suspended solids removed from the surface by washing. When water drops evaporate, mineral deposits are left in "spots". Compounding the spotting problem is the fact that when a window is being cleaned in sunlight, the surface of the window can be elevated to as much as 120.degree. F. Wash water in such circumstances evaporates quickly and can be seen to "steam" off of the window. Heavy and ultimately damaging mineral deposits can result.
Surface active agents (i.e. cleaning agents), such as polyphosphate and organic detergents, serve to spread adhering water drops over a wider area, making water spotting less noticeable. However, the effect is only cosmetic as the accumulation of hard mineral deposits as a whole is unaffected.
Although various automatic window washing devices have been described in the art (see, for example, U.S. Pat. No. 3,344,454 and 3,298,052), the inventor is not aware of any such devices which have proven to be practical or accepted in use. Such devices typically employ mechanical techniques to scrub the surface and to remove residual water. These cleaners suffer from a combination of several problems. First, many require some form of tracking (e.g., vertical mullions) on the building facade to guide the device up and down and maintain cleaning contact with the surface. Second, many include elaborate mechanical water collection and liquid removal apparatus, adding weight and expense to the overall device. Finally, since it is difficult to completely remove all of the wash water from the surfaces, and since all devices known to the inventor use common tap water (with or without detergents) as the washing medium, they tend to clean ineffectively, leaving mineral deposits from the tap water itself.
It would be an advance in the art if a window washing system were made which would be practical and effective in use and would avoid the need for persons to be suspended on scaffolding over the side of a building. It is accordingly an object of this invention to provide a washing system which can address the disadvantages of the prior systems.